group - a - anandgharu.files.wordpress.com · a two-pass assembler performs two sequential scans...

System Programming & OS Laboratory Third Year Computer Engineering

Pune Vidyarthi Griha’s COLLEGE OF ENGINEERING, NASHIK – 4 prepared by: prof. Gharu A. N.

GROUP - A

EXPERIMENT NO : 01

1. Title:

Design suitable data structures and implement pass-I of a two-pass assembler for

pseudo-machine in Java using object oriented feature. Implementation should consist

of a few instructions from each category and few assembler directives.

2. Objectives :

- To understand Data structure of Pass-1 assembler

- To understand Pass-1 assembler concept

- To understand Advanced Assembler Directives

3. Problem Statement :

Design suitable data structures and implement pass-I of a two-pass assembler for

pseudo-machine in Java using object oriented feature.

4. Outcomes: After completion of this assignment students will be able to:

- Implemented Pass – 1 assebmler

- Implemented Symbol table, Literal table & Pool table.

- Understood concept Advanced Assembler Directive.

5. Software Requirements:

Latest jdk., Eclipse

6. Hardware Requirement:

- M/C Lenovo Think center M700 Ci3,6100,6th Gen. H81, 4GB RAM ,500GB HDD

7. Theory Concepts:

Introduction :-

There are two main classes of programming languages: high level (e.g., C, Pascal)

and low level. Assembly Language is a low level programming language. Programmers

code symbolic instructions, each of which generates machine instructions.



An assembler is a program that accepts as input an assembly language program

(source) and produces its machine language equivalent (object code) along with the

information for the loader.

Figure 1. Executable program generation from an assembly source code

Advantages of coding in assembly language are:

Provides more control over handling particular hardware components

May generate smaller, more compact executable modules

Often results in faster execution

Disadvantages:

Not portable

More complex

Requires understanding of hardware details (interfaces)

Pass – 1 Assembler:

An assembler does the following:

1. Generate machine instructions

- evaluate the mnemonics to produce their machine code

- evaluate the symbols, literals, addresses to produce their equivalent machine

addresses

- convert the data constants into their machine representations

2. Process pseudo operations



Pass – 2 Assembler:

A two-pass assembler performs two sequential scans over the source code:

Pass 1: symbols and literals are defined

Pass 2: object program is generated

Parsing: moving in program lines to pull out op-codes and operands

Data Structures:

- Location counter (LC): points to the next location where the code will be placed

- Op-code translation table: contains symbolic instructions, their lengths and their op-

codes (or subroutine to use for translation)

- Symbol table (ST): contains labels and their values

- String storage buffer (SSB): contains ASCII characters for the strings

- Forward references table (FRT): contains pointer to the string in SSB and offset

where its value will be inserted in the object code

Figure 2. A simple two pass assembler.



Elements of Assembly Language :

An assembly language programming provides three basic features which simplify

programming when compared to machine language.

1. Mnemonic Operation Codes :

Mnemonic operation code / Mnemonic Opcodes for machine instruction eliminates the

need to memorize numeric operation codes. It enables assembler to provide helpful error

diagnostics. Such as indication of misspelt operation codes.

2. Symbolic Operands :

Symbolic names can be associated with data or instructions. These symbolic names can

be used as operands in assembly statements. The assembeler performes memory

bindinding to these names; the programmer need not know any details of the memory

bindings performed by the assembler.

3. Data declarations :

Data can be declared in a variety of notations, including the decimal notation. This avoids

manual conversion of constants into their internal machine representation, for example -5

into (11111010)2 or 10.5 into (41A80000)16

Statement format :

An assembly language statement has the following format :

[ Label] <Opcode> <operand Spec> [, operand Spec> ..]

Where the notation [..] indicates that the enclosed specification is optional.

Label associated as a symbolic name with the memory word(s) generated for the

statement

Mnemonic Operation Codes :



Instruction Format :

Sign is not a part of Instruction

An Assembly and equivalent machine language program :(solve it properly)

Note : you can also take other example with solution

Assembly Language Statements : Three Kinds of Statements

1. Imperative Statements

2. Declaration Statements

3. Assembler Directives

a) Imperative Statements : It indicates an action to be performed during the execution of

the assembled program. Each imperative statement typically translates into one machine

instruction.

b) Declaration Statements : Two types of declaration statements is as follows

[Label] DS

[Label] DC

<constant> ‘<Value>’


Pune Vidyarthi Griha’s COLLEGE OF ENGINEERING, NASHIK – 4 prepared by: prof. Gharu

A. N.

The DS (Declare Storage) statement reserves areas of memory and associates names with them.

Eg)A DS 1

B DS 150

First statement reserves a memory of 1 word and associates the name of the memory as A. Second statement reserves a memory of 150 word and associates the name of the memory as B.

The DC (Declare Constant) Statement constructs memory word containing constants.

Eg ) ONE DC ‘1’

Associates the name ONE with a memory word containing the value ‘1’ . The programmer can declare

constants in decimal,binary, hexadecimal forms etc., These values are not protected by the assembler. In

the above assembly language program the value of ONE Can be changed by executing an instruction

MOVEM BREG,ONE

c. Assembler Directives :

Assembler directives instruct the assembler to perform certain actions during the assembly of a

program. Some Assembler directives are described in the following

START <Constant>

Indicates that the first word of the target program generated by the assembler should be placed in

the memory word with address <Constant>

END [ <operand spec>]

It Indicates the end of the source program

Pass Structure of Assembler :

One complete scan of the source program is known as a pass of a Language Processor.

Two types 1) Single Pass Assembler 2) Two Pass Assembler.

System Programming & OS Laboratory Third Year Computer Engineering ``


Single Pass Assembler :

First type to be developed Most Primitive Source code is processed only once.

The operand field of an instruction containing forward reference is left blank intially

Eg) MOVER BREG,ONE

Can be only partially synthesized since ONE is a forward reference

During the scan of the source program, all the symbols will be stored in a table called

SYMBOL TABLE. Symbol table consists of two important fields, they are symbol name and

address.

All the statements describing forward references will be stored in a table called Table of

Incompleted Instructions (TII)

TII (Table of Incomplete instructions)

Instruction Address Symbol

101 ONE

By the time the END statement is processed the symbol table would contain the address of all

symbols defined in the source program.

Two Pass Assembler :

Can handle forward reference problem easily.

First Phase : (Analysis)

Symbols are entered in the table called Symbol table

Mnemonics and the corresponding opcodes are stored in a table called Mnemonic table

LC Processing

Second Phase : (Synthesis)

Synthesis the target form using the address information found in Symbol table.

First pass constructs an Intermediated Representation (IR) of the source program for use by

the second pass.



Data Structure used during Synthesis Phase :

1. Symbol table

2. Mnemonics table

Processed form of the source program called Intermediate Code (IC)

ADVANCED ASSEMBLER DIRECTIVES

1. ORIGIN

2. EQU

3. LTROG

ORIGIN :

Syntax : ORIGIN < address spec>

< address spec>can be an <operand spec> or constant

Indicates that Location counter should be set to the address given by < address spec>

This statement is useful when the target program does not consist of consecutive memory words.

Eg) ORIGIN Loop + 2

EQU : Syntax

<symbol> EQU <address spec>

<address spec>operand spec (or) constant



Simply associates the name symbol with address specification No

Location counter processing is implied

Eg ) Back EQU Loop

LTORG : (Literal Origin)

Where should the assembler place literals ?

It should be placed such that the control never reaches it during the execution of a program.

By default, the assembler places the literals after the END statement.

LTROG statement permits a programmer to specify where literals should be placed.

Note :(you can also write your own theory for this practical)

Solve the below example.for Pass-1 Assembler.

Algorithms :

Flowchart :



8. Conclusion :

Thus , I have implemented pass-1 assembler with symbol table, literal table and pool table.

References :

https://en.wikipedia.org/wiki/Assembly_language

http://freestudy9.com/one-pass-two-pass-assembler/

https://en.wikipedia.org/wiki/One-pass_compiler

http://enggedu.com/tamilnadu/university_questions/question_answer/be_am_2008/3th_sem/cse

/CS1203/part_b/12_a.html

NOTE : don’t write references.

A P C/W TOTAL SIGN

(3) (4) (3) (10)

A – Attendance, P – Performance , C/W – Completion & Writing

Oral Questions: [Write short answer ]

1. What is assembler.

2. Define system programming and its component.

3. State pass-1 and pass-2 assembler

4. What is forward reference & reverse references.

5. What is symbol table, literal table and pool table.

6. How pass-1 assembler works.

7. What is use of LTORG assembler directive.

https://en.wikipedia.org/wiki/Assembly_language

http://freestudy9.com/one-pass-two-pass-assembler/

https://en.wikipedia.org/wiki/One-pass_compiler

http://enggedu.com/tamilnadu/university_questions/question_answer/be_am_2008/3th_sem/cse/CS1203/part_b/12_a.html

http://enggedu.com/tamilnadu/university_questions/question_answer/be_am_2008/3th_sem/cse/CS1203/part_b/12_a.html

group - a - anandgharu.files.wordpress.com · a two-pass assembler performs two sequential scans...

Documents